1. Field of the Invention
The present invention relates to an optical module which is applied for an optical transceiver or the like to attach to and detach from the optical link
2. Related Background Art
In a high speed LAN (local area network), an optical transceiver is widely used as a module which converts between a digital electrical signal and an optical signal. There is an optical transceiver of an SFF (small form factor) type as a unified standard capable of size reduction in order to increase the number of ports of a hub apparatus or the like using the above-mentioned optical transceiver and to provide the ports at high density. This SFF type optical transceiver is characterized by small size and low power consumption, and furthermore, an SFP (small form factor pluggable) type optical transceiver capable of attaching and detaching an electrical connector without stopping an apparatus has been developed
In such small-sized optical transceiver, components are arranged in close proximity. Thus, when there are fluctuations in dimensions of the components, the components, a package and an optical subassembly in particular, may contact with each other, and in addition, the unexpected stress acting on the optical subassembly may cause misalignment of an optical axis or an increase in thermal stress during the use of the optical transceiver.
It is an object of the present invention to provide an optical module having a configuration capable of improving shielding properties, while preventing the excessive stress acting on the optical components.
In order to solve the above-mentioned subject, an optical module according to the present invention is an optical module comprising an optical unit including a metallic package having a cylindrical stem, a light emitting or receiving device contained in the metal package, a cylindrical sleeve located in a light input/output terminal, and a lead pin extended on the side opposite to the sleeve and connected to the device, a board having an electronic circuit connected to the lead pin, an electrically conductive bracket which covers the lead pin, and a housing which contains the optical unit and the board covered with the bracket, wherein an optical axis of the device aligns in line with the center axes of the cylindrical stem and sleeve, and wherein the bracket is disposed so that a part of the stem is exposed and an outer wall surface of the bracket which exposes the part of the stem is located inside a circumferential wall surface of the stem and close to the center axis of the stem in a diameter direction.
In the above-described configuration, the stem portion of the optical unit which is an optical subassembly is exposed through the bracket which covers and electrically shields the lead pin, and the housing is located outside the stem portion. Thus, the bracket is not located between the stem portion and the housing, and thus, it is possible to prevent the excessive stress acting on the optical unit without strictly setting manufacturing tolerances of structural components. Therefore, this makes manufacturing easier, thereby improving manufacturing yields and also simplifying an assembly step. Moreover, the bracket is present around the lead pin, so that the bracket functions as an electrical shield and thus improves in electrical properties.
Preferably, the bracket has a flat surface on the outer wall surface at the portion which exposes the stem. This makes it possible to manufacture the bracket easily, and also ensures that the stem portion of the optical unit can be exposed.
Preferably, the housing includes a metallic cover which covers a portion extending from the board to the optical unit through the bracket. This can ensure shielding properties of the stem portion exposed through the bracket.
Preferably, such board has a signal input/output terminal and a power terminal for an external apparatus, which are located on the side opposite to the side to which the optical unit is disposed. This facilitates connecting to an external circuit.
Preferably, the optical module comprises a plurality of optical units. Preferably, the optical module comprises, for example, a light emitting unit having a light emitting device, and a light receiving unit having a light receiving device. This configuration is suitable for a SFF or SFP type optical transceiver.